Process for the production of halogenated alcohols

ABSTRACT

An improved process for the production of a halogenated alcohol from an unsaturated alcohol and bromine which involves reacting the alcohol and bromine in aqueous lithium bromide of particular concentration, separating the product from the reaction medium, removing entrained lithium bromide from the product, and recycling the lithium bromide to the reaction.

Einited States Patent Thomas et al.

[451 Aug. 1,1972

[54] PROCESS FOR THE PRODUCTION OF HALOGENATED ALCOHOLS [72] Inventors:Robert M. Thomas; Robert P.

Levek, both of W. Lafayette, Ind.

[73] Assignee: Great Lakes Chemical Corporation,

West Lafayette, Ind.

[22] Filed: March 17, 1970 [21] Appl. No.: 20,404

[52] U.S. Cl ..260/633 [51] Int. Cl ..C07c 31/34 [58] Field of Search..260/633 [5 6] References Cited UNITED STATES PATENTS 3,283,013 6/1966Rimmer ..260/633 3,378,593 4/1968 .lenkner et a1. ..260/633 3,268,5978/1966 Clemons et a1. ..260/633 FOREIGN PATENTS OR APPLICATIONS1,132,034 10/1968 Great Britain ..260/633 1,492,303 7/1967 France..260/633 1,230,412 12/1966 Germany ..260/633 Primary Examiner-Howard T.Mars Att0rneyGordon W. Hueschen and Talivaldis Cepuritis 5 7] ABSTRACTAn improved process for the production of a halogenated alcohol from anunsaturated alcohol and bromine which involves reacting the alcohol andbromine in aqueous lithium bromide of particular concentration,separating the product from the reaction medium, removing entrainedlithium bromide from the product, and recycling the lithium bromide tothe reaction.

11 Claims, No Drawings PROCESS FOR THE PRODUCTION OF HALOGENATEDALCOHOLS This invention pertains to an improved process of producing abrominated alcohol from bromine and an unsaturated alcohol, and isespecially concerned with an improved method of making 2,3-dibromo-1-propanol by the reaction of bromine and allyl alcohol in the presence ofaqueous lithium bromide of a particular concentration range.

BACKGROUND OF THE INVENTION The brominated alcohols obtained by theprocess of this invention are intermediates useful, when reacted withphosphorous oxychloride, in the preparation of flame retardants asdescribed in the U.S. Pat. No. 3,268,597.

It is already known to produce a number of these dibrominated alcoholsby the reaction of bromine and an unsaturated alcohol. In particular itis well known to produce 2,3-dibromo-1-propanol by the reaction ofbromine and allyl alcohol (U.S. Pat. Nos. 3,268,597; 3,283,013;3,378,593 and German Pat. No. 1,089,743). It is also known that lithiumbromide (LiBr) is a material which can be present in the reaction mediumand which enters into the reaction to reduce formation of1,2,3-tribromopropane, l-IBr, and other by-products (see U.S. Pat. No.3,283,013). Metal chlorides have also been added into a reaction betweenchlorine and allyl alcohol in the production of 2,3-dichloro-l-propanol, ostensibly to permit higher yields and reduceformation of undesired 1,2,3-trichloropropane and other by-products(British Pat. No. 570,374). Similar procedures are known wherein othermaterials are added to the reaction for purposes of reducing theformation of undesirable by-products, for example, to reduce formationof undesired 1,2,3- tribromopropane and HBr in a reaction betweenbromine and allyl alcohol. Such materials include basic oxides, neutralor acid carbonates, salts of lower fatty acids, and basic 'ionexchangers (German Pat. specification No. 1,089,743). All of these addedmaterials enter into the reaction in one way or other to reduce theformation of 1,2,3-tribromopropane, I-IBr, and other by-products andthereby permit more advantageous production of 2,3-dibromo-propan-l-olfrom the reaction between bromine and allyl alcohol. Where LiBr has beenused for such purpose previously, it has been used in relatively diluteorganic solutions. (See U.S. Pat. No. 3,283,013.) Reported yields havebeen ninety percent (90 percent) of the desired 2,3- dibromo-l-propanol.The LiBr solution suggested in U.S. Pat. No. 3,283,013 is an organicsolution, for example, a carbon tetrachloride solution, which isspecifically exemplified. Polar solvents having hydroxyl groups, whichinclude water, are specifically excluded as undesirable because ofreactions with bromine or intermediates in the bromination reaction, orbecause these polar solvents have been suspected of causing reactionbetween other solvents and bromine or intermediates in the brominationreaction. (U.S. Pat. No. 3,283,013, column 3, line 31.) Where aqueoussolutions have been employed in an analogous reaction, yields of desired2,3-dichloro-l-propanol have been considerably lower, on the order of40-50 percent, presumably because of the formation of undesiredbyproducts. (See Example 11, British Pat. No; 570,374.)

The non-aqueous process with its obvious advantages previously disclosedin the art has therefore appeared as a superior and advantageousreplacement for the aqueous process.

It has now been found that still greater advantages, and especiallyadvantages of further increased yields and purer product, are attainableby the employment of aqueous LiBr solutions having a particular range ofconcentration, about 45-65 percent aqueous LiBr solutions, which areintroduced into the reaction between the bromine and allyl alcohol inthe usual manner. However, in the present process the desired 2,3-dibromo-l-propanol product is separated from the aqueous phase of thereaction and LiBr entrained or contained therein is removed, as bywashing with water, to give a relatively dilute LiBr solution. Theproduct may then be further treated as by distillation or vacuum dryingto provide the product in finally purified form. The relatively diluteaqueous LiBr solution, on the other hand, is then concentrated to aconcentration within the desired range, about 45-65 percent, andreturned or recycled to the reaction zone.

When operating according to this procedure, which has not previouslybeen suggested by the prior art, involving a specified concentration ofaqueous LiBr solution, recovery of LiBr from the organic product as bywashing with water, concentration of the thus-obtained LiBr solution,and recycling thereof into the reaction, unprecedented yields of thedesired 2,3-dibromo-lpropan-l-ol are obtained. The desired product ismoreover obtained in this matter in such a high yield and purified statethat it can, if necessary or desirable, be further purified in anextremely simple manner, as by vacuum drying.

The provision of a process having the foregoing procedural steps andproviding the foregoing enumerated advantages is accordingly an objectof the present invention.

Other objects and advantages of this invention will become apparenthereinafter and still others will be obvious to one skilled in the art.

SUMMARY OF INVENTION This invention contemplates an improved process ofpreparing alcohols by the simultaneous addition of bromine and anunsaturated alcohol, diol, or polyol, including triols and the like,having at least three carbon atoms, preferably three to seven carbonatoms, inclusive, to a 45-65 percent aqueous lithium bromide solution ina reaction zone at a temperature of about 20 to C. to provide aresulting brominated product which is insoluble in the aqueous lithiumbromide phase. The brominated alcohol product is separated from theaqueous reaction medium and entrained lithium bromide removed therefrom,preferably by washing with water. The lithium bromide solution,preferably including the wash, is then concentrated to the extentnecessary to attain a concentration of about 45-65 percent aqueouslithium bromide and recycled to the reaction zone together with startingunsaturated alcohol and bromine. The brominated alcohol is furtherpurified, as by distillation, but is usually sufficiently pure that itcan be finally purified using only vacuum drying.

DESCRIPTION OF PREFERRED EMBODIMENTS I. Reactants The starting alcohols,diols, and polyols contemplated for use in producing brominated alcoholsin this invention are water-soluble alcohols, preferably of the allylictype having three to seven carbon atoms, preferably three to four carbonatoms, inclusive, and most preferably 3-carbon atoms, such as2-buten-l,4 diol; 3-buten-l,2-diol; 2-butyn-l,4-diol; 3-butyn- 1,2Diol;2-propyn-l-ol; 2-propen-l-ol; 2-methyl- 2- propenl -ol4-pentene-l,2,3-triol; 4-hexene-l ,2 ,3-tn'ol; Z-hydroxymethyl- 21-01; Z-butenl-ol;3-butenl-ol; and 4-penten-2-ol. In the preferred embodiment theunsaturated alcohol is 2-propen-l-ol, commonly known as allyl alcohol.The alcohols used in the process of this invention can be commercialgrade material. The reaction medium of this invention is relativelyinsensitive to traces of water present in the commercial grade alcohols.In like manner the bromine and lithium bromide used in the process ofthis invention can be commercial grade reactants and need not bespecially purified or prepared.

II. Operative Limits A. Reaction Temperatureperating temperatures forthe reaction of this invention are usually between about 80 C. with thepreferred operating range being about 60 C. A slightly better qualityproduct can frequently be obtained by operating at temperatures lowerthan 30 C., but at such temperature viscosity and heat transfer problemsincrease to such a point that they sometimes become a limiting factor.It is preferred to increase the operating temperatures as theconcentration of the LiBr solution is increased. The rate of productionof product is dramatically increased at temperatures between 60 C. and80 C. However, entrainment and solubility of lithium bromide solution inthe brominated product also increases as the temperature increases.

B. AlcoholrLithium Bromide RatioConcentration of alcohols in the lithiumbromide solution is usually kept as low as possible since'the alcohols,which include both the starting material and final product, can react toform undesirable by-products, which are more highly brominated products,such as l,2,3- tribromopropane, HBr, and also alcohol ethers. One sidereaction by which undesired high-boiling alcohol ethers is formed hasthe following reaction sequence.

CH2: crrcrnorr m cin loncnpon Br OR r ROH 'oII2o1-r-orn-o1r b1n o1r-c1n0n 0R Br nm It is therefore desirable to supress formation of H Br inthe reaction. lt is one finding of this invention that HBr production iseffectively curtailed by the employment of a concentrated aqueouslithium bromide solution according to the manner of the invention.

In the procedure of the present invention, the alcohol and bromine aresimultaneously added to a reaction zone containing aqueous concentratedlithium bromide, the reaction product formed is removed, preferablyneutralized and washed, and the recovered lithium bromide isconcentrated and recycled to the reaction zone. The product can bepurified in usual manner, but if aqueously washed free of lithiumbromide, can be purified either by distillation or vacuum drying.

It is preferred that the unsaturated alcohol and bromine are added atapproximately the same rate so that all the alcohol substantially reactson addition. This maintains a low ratio of alcohol to lithium bromide inthe solution. As the concentration of alcohol builds up in the lithiumbromide solution, the amount of l-lBr produced also increases, therebyreducing the ultimate yield and purity of the product. The alcoholswhich affect the reaction include the 2,3-dibromopropan-l-ol product,since it is itself an alcohol. It is therefore naturally preferred thatthe product be removed as soon and completely as possible so as tomaintain a low ratio of total alcohols to lithium bromide. Under mostpreferred operating conditions, it is not advisable to have a totalalcohol concentration of more than 15 percent. Under optimum conditionsall final product, except the amount soluble in the medium, is removedfrom the lithium bromide and the product removed is substantially pureproduct containing only minor amounts of lithium bromide which aresoluble in the product. In those reactions wherein allyl alcohol is areactant, it has been found that about 2-4 percent (w/w) of2,3-dibromopropan-l-ol is soluble in the aqueous lithium bromide medium.However, in actual practice, an amount of product and starting materialamounting in total, including dissolved product, even up to 25 percentby weight of the medium can be and frequently is entrained in themedium. Conse-quently, the lithium bromide solution always contains someentrained final product in addition to dissolved product necessitatingseparation of solution from final product for obvious reasons ofeconomy. In addition, a certain amount of lithium bromide solutionbecomes entrained in the final product and must be removed therefrom.This can most effectively be accomplished by aqueously washing the finalproduct. The aqueous lithium bromide wash recovered in this step isusually concentrated and returned to the reaction zone along with freshaqueous lithium bromide.

C. Water:Lithium Bromide RatioAs stated, the formation of HBr should belimited to prevent formation of undesired by-products. Low ratios oflithium bromide to water fail to prevent side reactions and lead tocompetitive reactions. Formation of HBr is suppressed when theconcentration of the aqueous lithium bromide is at least 45 percent(w/w). Concentrations of aqueous lithium bromide as high as percent canbe used, but high concentrations require higher operating temperatures.It is therefore preferred to use a concentration of about 45-65 percentand most preferably a concentration of 50-60 percent (w/w) aqueouslithium bromide. At a concentration of 55 percent or higher, theformation of HBr is negligible and therefore produces substantially noside reactions. The concentrated aqueous lithium bromide solution,because of its extremely high affinity for bromine, allows ionicbromination to be carried out at temperatures above the boiling point ofbromine (b.p. 58.8 C.) with negligible losses of bromine due tovolatilization. ln addition, the liquid reaction medium with a low vaporpressure and low freezing point permits ease of handling in separationand recycling procedures. Table I shows the physical properties of someconcentrated solutions of lithium bromide.

TABLE I Physical Properties of Aqueous Lithium Bromide Solutions(w/w)LiBr b.p. c. f.p. C.

The aqueous lithium bromide medium is moreover relatively insensitive totraces of water present in commercial starting material and alsorelatively hydrolytically stable during the reaction and recoveryoperations, whereas certain other hydrolytically stable inorganicbromides are not sufficiently soluble in water so as to form comparablebromide concentrations and yet remain in the form of a liquid underoperating conditions.

Recycled aqueous lithium bromide reaction medium which has passedthrough the reaction zone at least once provides a higher yield ofdesired product with less formation of undesirable by-products than afresh stock of the aqueous medium. In the practice of the invention, theaqueous lithium bromide reaction medium, after start-up, issubstantially recycled material to insure highest yields and purestproduct.

D. BrominezAlcohol Ratio-The process can be operated using substantiallyequimolar quantities of bromine and unsaturated alcohol. Purification ofthe product is simplified by carrying out the process using an excess ofalcohol in an amount of l-5 mole percent relative to the amount ofbromine employed.

The process can be operated as a batch, semi-continuous, or continuousprocess. Preferably the process is carried out as a continuous processwhich operates in the following manner to produce 2,3-dibromopropanl-olfrom allyl alcohol.

A reaction zone is charged with a 45-65 percent (w/w) aqueous lithiumbromide and maintained at 5060 C. Bromine and allyl alcohol are addedsimultaneously to the reaction zone. The allyl alcohol can be addeddissolved in recycled stock of aqueous lithium bromide medium. The2,3-dibromopropan-l-ol is only slightly soluble in the lithium bromidereaction medium and therefore immediately forms a separate layer whichis constantly removed from the aqueous medium. The crude product istransferred to a washing zone wherein lithium hydroxide or lithiumcarbonate is added, together with water wash, to neutralize traces ofHBr. The wash water is in the amount of approximately 10 percent (w/w)based on crude product. This results in a total recovered lithiumbromide solution of approximately 30 percent (w/w) concentration. Thedilute lithium bromide solution is then concentrated to 45-65 percentLiBr by weight and recycled to the reaction zone. The crude product isfurther worked up by known procedure. The purification can be bydistillation, as is well-known in the art, or by vacuum dryingtechniques. Because of the uniquely pure product produced by the presentprocess, the vacuum drying technique is ordinarily sufiicient to preparean extremely pure product.

Having generally described the process of the invention, the followingexamples are presented as illustrative of the best mode contemplated bythe inventors for carrying out the invention. These examples are not tobe construed as limiting.

EXAMPLE 1 Allyl alcohol (58.7 g., 1.01 mole, commercial grade) and 159.8g. (1.00 mole) of bromine are simultaneously added with agitation to 800ml. of 60 percent (w/w) aqueous lithium bromide solution at a reactiontemperature of 35-40 C. The aqueous lithium bromide solution is preparedby dissolving anhydrous lithium bromide in water to the desiredconcentration.

After the simultaneous addition is complete, agitation is stopped andthe organic phase (bottom layer) is separated from the reactor. Aquantity of freshly prepared 60 percent (w/w) lithium bromide solution(25 g.) is then added to the reactor to replace aqueous lithium bromidemedium lost by solubility and entrainment in the organic phase. A secondcharge of bromine and allyl alcohol is then added as above and theprocedure repeated. This procedure of simultaneous addition of bromideand allyl alcohol, separation of organic phase, and replenishment ofaqueous lithium bromide medium is repeated until a total of 21 moles ofbromine are reacted. The total amount of 60 percent (w/w) lithiumbromide added is 500.0 .g. lithium bromide solution per 5,160.6 g. ofcrude organic phase.

The fractions of separated organic phase of the above processes arecombined and washed with two portions of water equalling 10 percent(w/w) of the organic charge. The first wash is neutralized to a pH of 7by the addition of lithium carbonate. The washed neutralized2,3-dibromopropan-1-ol is dried in vacuo at C. at 1 1 mm. pressure fortwenty minutes.

Analytical data on vacuum-stripped material:

2,3-dibromopropan-l-ol, 99.8% (determined by vapor phase chromotographyassay (VPC) 1,2,3 -tribromopropane, 0.07% (VPC) Acid Number-- 0.03 APHAMicro-analysis: Bromine:

Theory: 73.3% Found: 73.6%

High-boi1ing residue (residue remaining on distillation of an aliquot at80 C./O.1-O.4 mm) 0.7%

Water (w/w) 0.08%

Hydroxyl number 255 Yield (Stripped only product) 95.5% based on allylalcohol Distillation of an aliquot of the washed and neutralized2,3-dibromopropan-l-ol produces a colorless product. of the followingassay:

2,3-dibromopropan-l-ol 99.9% (VPC) Acid Number- 0.02

Water-0.01% (w/w) High boiling residuenegligible l-lydroxyl number-257Yield based on allyl alcohol-94.7%

EXAMPLE 2 The process described in Example 1 is repeated except that thetwo portions of wash water derived from the purification of the crudeproduct in Example 1 are combined and concentrated in vacuo to provide areconcentrated lithium bromide solution containing 62 percent (w/w)lithium bromide (determined by Mohr titration sp. gr. 1.77 (22 C.)) andthis recycled lithium bromide solution is used as make-up in the mannerdescribed in Example 1 instead of fresh 60 percent (w/w) lithiumbromide.

Analytic data: After vacuum drying product: 2,3-dibromopropanol 99.7%(VPC Assay) Tribromopropane 0.08% (VPC Assay) Acid Number 0.03

Water 0.05% (w/w) APHA 90 High boiling residue 0.7% (w/w) Hydroxyl No.255

Yield (vacuum stripped only) 97.5% based on allyl alcohol.

According to this procedure, the use of recycled lithium bromidesolution provides a 2 percent or better increase in yield with no lossin purity of product. By means of this process, using a concentratedlithium bromide solution as the reaction medium and recycling thelithium bromide solution, a crude product is obtained which containsless than 1 percent organic contaminates and may be purified to a gradeof product useful as an intermediate by simple vacuum drying technique.

EXAMPLE 3 Examples 1 and 2 illustrate a semi-continuous process. Theprocess can be operated in a continuous manner by continuously removingthe organic phase and continuously adding fresh bromine and allylalcohol. In a continuous process there is a greater amount of reactionmedium entrained with the crude product. This entrained medium isseparated in a separator before the crude product is processed asdescribed above. Separated medium and lithium bromide solution retrievedfrom the wash step are concentrated and continuously added to thereactor to maintain a substantially constant level in the reactor.

EXAMPLE 4 The process is operated in a batchwise manner by adding thereagents in the total amount specified in Example l to a vessel. Thereaction mass is agitated for minutes and then diluted with water (about10 percent w/w based on organic phase). The reaction mass is neutralizedwith lithium hydroxide to a pH of 7. The organic phase is removed andthe aqueous phase containing approximately 30 percent (w/w) lithiumbromide is concentrated in vacuo to 60 percent (w/w) lithium bromide andreused for subsequent batches. It is recognized that some control overthe total alcohol/LiBr solution ratio is sacrificed by operating in abatchwise manner, but in such operation the product obtained by usingrecycled LiBr as the medium is nevertheless characterized by higheryields than the product obtained from fresh LiBr solution, although notas pure as in a continuous or semi-continuous process where thealcohol/LiBr ratio can be kept lower and more carefully maintained.

It is to be understood that the invention is not to be limited to theexact details of operation or procedures shown and described, and theinvention is therefore to be limited only by the full scope of theappended claims.

What we claim is:

1. In a process for the preparation of a brominated alcohol by thereaction of bromine and an unsaturated alcohol selected from the groupconsisting of watersoluble monohydroxy and polyhydroxy alkenes andalkynes having 3-7 carbon atoms inclusive, the improvement comprisingthe steps of concurrently adding bromine and said unsaturated alcohol toan about 45-65 percent aqueous solution of lithium bromide at a emrature 0 about 20-80 se arat' brominated alcoiiol product from the liihlum romid solution and recovering the same, and reusing said lithiumbromide solution in a subsequent reaction of the same kind.

2. A process according to claim 1 wherein said separated lithium bromidesolution is concentrated to the extent necessary to attain an about45-65 percent lithium bromide concentration.

3. A process according to claim 1 comprising separating brominatedalcohol, as an organic phase, from lithium bromide solution, as anaqueous phase, aqueously washing said organic phase to remove remaininglithium bromide, recovering brominated alcohol from said aqueous wash,concentrating said aqueous phase including aqueous wash to a lithiumbromide concentration of about 45-65 percent, and returning saidconcentrated lithium bromide solution to the reaction zone with startingunsaturated alcohol and bromine.

4. A process according to claim 3 wherein the alcohol is allyl alcohol.

5. A process according to claim 4 wherein the reaccontinuously removingthe 2,3-dibromopropan-l-ol organic phase formed, aqueously washing saidorganic phase and recovering dilute aqueous lithium bromide and2,3-dibromopropan-l-ol from said wash, concentrating said recoveredaqueous lithium bromide to a 50-60 percent lithium bromide solution, andreturning said recovered aqueous lithium bromide to the reaction zone inan amount sufficient to maintain a substantially constant volume oflithium bromide solution therein.

9. A process according to claim 8 wherein the allyl alcohol is added in1-5 mole percent excess relative to the amount of bromine added.

10. A process according to claim 8 wherein the 2,3- dibrornopropan-l-olremoved from the reaction medium is neutralized with lithium hydroxideor lithium carbonate.

11. A process according to claim 10 wherein the recovered2,3-dibromopropan-1-ol is purified by vacuum drying.

UNITED STATES PAT ENT OFF CETIFECATE F i Patent No. 3,681,468 DatedAugust 1, 1972 Inventor(s) Robert M. 'Ihcmas and Robert P. Levek It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, lines 8, 9 and 10 should read as follows:

-- l,2diol; 2-propyn-l-ol; 2-propen-l-ol; 2-methyi-2- propen-l-ol; 4pentene-l 2 3-triol 4-hexene-l 2 3-triol; 2hydroxymethyl-2 propenl-ol';Z-buten-l-ol; 3-buten- Signed and sealed this 9th day of January 1973(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting 0f ficer aCommissioner (pf-Patents FORM PO-105O (10-69) r d aoammagr U.S.GOVERNMEhT PRINTlNG bFFICE 969 0-366-334 I

2. A process according to claim 1 wherein said separated lithium bromidesolution is concentrated to the extent necessary to attain an about45-65 percent lithium bromide concentration.
 3. A process according toclaim 1 comprising separating brominated alcohol, as an organic phase,from lithium bromide solution, as an aqueous phase, aqueously washingsaid organic phase to remove remaining lithium bromide, recoveringbrominated alcohol from said aqueous wash, concentrating said aqueousphase including aqueous wash to a lithium bromide concentration of about45-65 percent, and returning said concentrated lithium bromide solutionto the reaction zone with starting unsaturated alcohol and bromine.
 4. Aprocess according to claim 3 wherein the alcohol is allyl alcohol.
 5. Aprocess according to claim 4 wherein the reaction temperature is about30*-60* C.
 6. A process according to claim 1 wherein the concentrationof lithium bromide in the aqueous solution is about 50-60 percent.
 7. Aprocess according to claim 6 wherein the allyl alcohol added is in 1-5mole percent excess relative to the amount of bromine added.
 8. Aprocess according to claim 1 which comprises continuously andsimultaneously adding bromine, allyl alcohol, and aqueous lithiumbromide solution to a reaction zone maintained at 30*-60* C. andcontaining a 50-60 percent aqueous lithium bromide solution,continuously removing the 2,3-dibromopropan-1-ol organic phase formed,aqueously washing said organic phase and recovering dilute aqueouslithium bromide and 2,3-dibromopropan-1-ol from said wash, concentratingsaid recovered aqueous lithium bromide to a 50-60 percent lithiumbromide solution, and returning said recovered aqueous lithium bromideto the reaction zone in an amount sufficient to maintain a substantiallyconstant volume of lithium bromide solution therein.
 9. A processaccording to claim 8 wherein the allyl alcohol is added in 1-5 molepercent excess relative to the amount of bromine added.
 10. A processaccording to claim 8 wherein the 2,3-dibromopropan-1-ol removed from thereaction medium is neutralized with lithium hydroxide or lithiumcarbonate.
 11. A process according to claim 10 wherein the recovered2,3-dibromopropan-1-ol is purified by vacuum drying.